1. Field of the Invention
The present invention relates to an optical disk device in which jump control is performed so as to make a light beam irradiating position move to an adjacent recording track at every rotation of an optical disk.
2. Description of Related Art
In an optical disk device, a data is recorded or reproduced by irradiating a recording track on an optical disk with a light beam such as a laser beam and receiving a reflected light beam from the recording track. In such an optical disk device, an on-track control is performed for holding a light beam irradiating position on a desired recording track, and a focus control is performed for focusing the light beam on the recording track. In recording or reproducing, a seek control is performed for moving the light beam irradiating position from the currently irradiating recording track that is held by the on-track control to another desired recording track.
For the on-track control and the seek control, the light beam irradiating position is required to be moved along the direction of the radius of the optical disk (hereinafter referred to as the radial direction). An optical head for emitting the light beam has, as means for moving the light beam irradiating position in the radial direction, an actuator for changing the position of an objective lens opposing the optical disk and another actual, or for moving the entire optical system in the radial direction. For the on-track control where the light beam irradiating position is moved by a small distance, the former actuator is used, and for the seek control where the light beam irradiating position is moved by a long distance across a plurality of recording tracks, the latter actuator is used.
The recording track on a general optical disk, however, is outwardly formed in a spiral shape, and hence, when the on-track control is performed on the spirally formed recording track, the light, beam irradiating position is gradually moved outward as the optical disk rotates. A data is recorded in or reproduced from a given area on art optical disk in many cases. Therefore, in order to shorten an access time of the optical head in the recording/reproducing operation, the light beam irradiating position is desired to maintain its current position.
Due to the above-mentioned fact, in a conventional optical disk device, jump control is performed so as to allow the light, beam irradiating position to jump to the inner adjacent recording track at each rotation of the optical disk during a wait period between the recording/reproducing operations. The jump control can be regarded as a kind of the seek control because the light beam irradiating position is moved between the recording tracks. For the jump control, however, the actuator used for the on-track control is utilized because the light beam irradiating position is limited to jump the distance bet,ween the adjacent recording tracks and the on-track control is naturally canceled for performing the jump control.
In a writable optical disk device, it is necessary to return the light beam irradiating position to the previous recording track in performing the reproducing operation for confirming the recorded contents. The jump control is performed also in such a case.
FIG. 1 is a diagram showing the configuration of a mechanism for driving an objective lens in an ordinary optical head. As strewn in FIG. 1, an objective lens 10 of the optical head is fixed on a lens holder 12, which is penetrated by a supporting axis 11. The supporting axis 11 has an axial center that is substantially vertical to the recording surface of an optical disk (not; shown) disposed above the supporting axis 11. The supporting axis 11 is penetrated through the lens holder 12 so that the lens holder 12 slide along the axial length direction and be movable around the axial center of the supporting axis 11. The objective lens 10 is fixed on the lens holder 12 so that the optical axis of the objective lens 10 be parallel to the axial center of the supporting axis 11 and, namely, be vertical to the recording surface of the optical disk.
Below the objective lens 10 is disposed a starting mirror 13. The starting mirror 13 reflects a light beam emitted by a fixed optical system (not shown) in the direction parallel to the optical axis of the objective lens 10 so as to lead the reflected light beam to the optical disk, and also reflected s a light beam, which has reflected by the optical disk to proceed along the optical axis of the objective lens 10, in the reverse direction, so as to lead the reflected light, beam to the fixed optical system. A data is recorded or reproduced by using the light beam as a medium.
On the outer surface of the lens holder 12 are provided a focus actuator 14 to be used for the focus control and a track actuator 15 to be used for the on-track control and the jump control.
The focus actuator 14 comprises a pair of, i.e., N and S, permanent magnets aligned along the axial length direction of the supporting axis 11 and a driving coil on the side of the magnets closer to the supporting axis 11. When the driving coil is supplied with power, a force along the axial length direct ion of the supporting axis 11 is applied to the lens holder 12 in a magnetic field formed by the permanent magnets. Due, to the force, the objective lens 10 fixed on the lens holder 12 is displaced toward or away from the optical disk so as to focus the light beam on a recording track on the optical disk. Thus, the focus control is performed by control of supplying power to the focus actuator 14.
The track actuator 15 also comprises a pair of, i.e., N and S, permanent magnets aligned vertically to the axial length direction of the supporting axis 11 and a driving coil on the side of the magnets closer to the supporting axis 11. When the driving coil is supplied with power, a force in the direction of a tangent line of the supporting axis 11 is applied to the lens holder 12 in a magnetic field formed by the permanent magnets. Due to the force, the lens holder 12 is rotated around the axial center of the supporting axis 11, thereby displacing the objective lens 10 fixed on the lens holder 12 in a plane substantially parallel to the recording surface of the optical disk. Thus, the on-track control and the jump control are performed by displacing the objective lens 10 through the control of supplying power to the track actuator 15 so that the light beam irradiating position on the optical disk can be moved in the radial direction.
The above-described, conventional jump control is generally conduced by the following procedure: For the movement of the light beam irradiating position by a known distance between the adjacent recording tracks, an acceleration time for the optical bead and an equivalent deceleration time are previously set. The track actuator 15 is supplied, at each rotation of the optical disk, with a jump signal including an acceleration signal and a deceleration signal respectively corresponding to the set acceleration and deceleration Lime.
In this method, the behavior of the track actuator 15 in response to the jump signal is assumed to be uniform. The track actuator 15, however, is actually affected by unstable external forces such as a friction resistance between the supporting axis 11 and the lens holder 12 and a resistance of an extension line for supplying power to the driving coil. In addition, mechanical deviation can be caused in the position of the center of gravity of the lens holder 12, a winding resistance of the driving coil and the positions to mount, the driving coil and the permanent magnets. Accordingly, the behavior characteristics of the track actuator 15 cannot be prevented from varying from one optical disk to another.
Therefore, the processing accuracy and the assembling accuracy of each part of the track actuator 15 is conventionally increased so as to decrease the mechanical deviation as much as possible. The remaining causes of deviation, which cannot be canceled by increasing the accuracy, is absorbed by initially adjusting the continuation time of the acceleration signal and the deceleration signal in the control system of the jump control, so as to perform the jump control accurately. This results in a decrease in productivity of the optical disk devices, and is one of the factors to prevent the decrease of the production cost of the optical disk devices.
Further, even when the above-mentioned countermeasure is taken, the behavior characteristic of the track actuator 15 is varied by external factors such as the change of the surrounding environment in actual use and the variation of the power supply voltage, and is also varied with time. Accordingly, it is difficult, to continuously perform appropriate jump control for a long period of time.
Japanese Patent Application Laid-Open No. 3-173939 (1991) discloses a method for a jump control. In this method, the light beam irradiating position is detected to be passed through a middle point between the tracks to be jumped, during the jumping operation in response to an acceleration signal, and the acceleration signal is switched to a deceleration signal in response to the detection of the passage. In this manner, by varying the jumping state based on the actual operation of the track actuator 15, the mechanical deviation is canceled, thereby complying with the variation of the behavior characteristic due to the external factors or with time. This method, however, has a disadvantage that an error can be caused in the position of the light beam irradiating position after finishing the acceleration due to the delay of the rise of the deceleration signal and the speed before switching the acceleration signal.
The aforementioned Japanese Patent Application Laid-Open No. 3-173939 (1991) also discloses to suspend the generation of the deceleration signal in response to the detection of arrival of the light beam irradiating position at a target track during the deceleration operation. This means that an error is caused in the stop position of the light beam irradiating position as described above. Even when the deceleration signal is suspended when the light beam irradiating position reaches the target track, an error can still be caused. Thus, accurate jump control cannot be realized by such a method.